1. Field of the Invention
The present invention relates to communication terminal devices that can be used in, for example, radio frequency identification (RFID) systems in which communication is performed with external appliances via electromagnetic signals.
2. Description of the Related Art
In recent years, RFID systems utilizing an HF band, of for example, 13.56 MHz have been widely used as FeliCa (registered trademark) and near field communication (NFC) systems. For example, an antenna device for an RFID system is disclosed in Japanese Patent No. 3975918.
FIG. 1 is a sectional view of an antenna device section of a communication terminal device 90 described in Japanese Patent No. 3975918. This antenna device includes an asymmetrically shaped coil in which the winding intervals at two positions that face each other across a central portion of the winding region of the coil 71 have been made to be different from each other. At a large winding interval side 71a, a magnetic body 72 is arranged on a surface of the coil 71 opposite to an input-unit-94-side surface, which faces an IC card 1, of the coil 71, and at a small winding interval side 71b, the magnetic body 72 is arranged on the input-unit-94-side surface, which faces the IC card, of the coil 71. A reader/writer circuit 50 is connected to the coil 71. The antenna device is arranged in an antenna housing concavity 97a formed in a metal case 97 and is protected by a resin member 98. The magnetic field distribution of the antenna device is a distribution whose asymmetricity is more pronounced on the side 71a at which the winding interval and the line width of the coil 71 are larger. Consequently, a preferable communication state can be secured in a direction orthogonal to a main surface of the antenna device.
However, in an antenna arranged such that two conductor portions, which face each other across the central portion of the winding region of the coil conductor, are wound around a magnetic core, since the actual direction of the winding center axis of the coil conductor is neither parallel to or nor orthogonal to the main surface of the magnetic core but is tilted, there has been a problem in that it has been difficult to orient the directivity in a predetermined direction.
The antenna device of Japanese Patent No. 3975918 illustrated in FIG. 1 includes an asymmetrically shaped coil in which the winding intervals at two positions that face each other across a central portion of the winding region of the coil have been made to be different from each other and thereby the direction of magnetic flux is controlled. It is assumed that this antenna device will perform communication at a very short distance such as in communication with an RFIC card. For example, in the case where a leading end of a cellular phone terminal is brought close to a reader/writer in order to perform communication between the cellular phone terminal and the reader/writer, an antenna device is arranged in a leading end portion of the casing of the cellular phone terminal.
However, usually, it is often the case that other functional components such as, for example, a GSM or CDMA cellular phone antenna are arranged in the cellular phone terminal. Therefore, there are often restrictions on the arrangement of an antenna device in the leading end portion inside the cellular phone terminal casing. In addition, when another functional component arranged in the leading end portion is a cellular phone antenna, there are cases where the closer the arrangement position of the antenna device is to the leading end portion, the more the antenna device affects the antenna characteristics of the cellular phone antenna. On the other hand, there are cases where, provided that the antenna device is arranged at a position that is spaced away from the cellular phone antenna, it can be ensured that the two antennas are isolated from each other, but depending on the size of the terminal device, the layout becomes difficult. In addition, there are cases where, along with there being restrictions on the layout on the antenna device, there are also restrictions on the directivity direction of the antenna device.
For example, in the case where the antenna device is arranged in a trailing end portion, which is another end portion on the opposite side to the leading end portion, the antenna gain at the time of use when the leading end of the cellular phone terminal is held over the reader/writer, is inevitably reduced.
In addition, in the case where two cellular phone terminals are brought close to each other in order to perform communication, communication is performed in a state where the leading end portions of the two terminals are brought close to each other, and the same problem also occurs in this case.